Coolant system pressure
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Tuned
Joined: Apr 2019
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Coolant system pressure
Hello all,
Does anyone know the correct radiator cap pressure for a 1977 F250 with a 460 and a super cooling radiator? My bypass hose blew last weekend and I'm sure the hose was old, but I thought I'd double check because I replaced the original radiator this year and just used the new cap that came with the radiator. I think it's a 13 psi cap.
Does anyone know the correct radiator cap pressure for a 1977 F250 with a 460 and a super cooling radiator? My bypass hose blew last weekend and I'm sure the hose was old, but I thought I'd double check because I replaced the original radiator this year and just used the new cap that came with the radiator. I think it's a 13 psi cap.
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Tuned
Joined: Apr 2019
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It definitely blew. Big rip down the side of it. Thanks for the answer.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
This is not necessarily a good idea. The OP is discussing a 1977 product year, which may be OK. It's not necessary to "proof test", if it shipped with a 13 pound cap, I would not exceed that without good reason and I can't think of any. Depends on what you mean by "vintage", but the earlier designs will almost guarantee a blown out radiator, they are not capable of more than 4 or 5 psi, my '64 uses a 7 lb cap.
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Tuned
Joined: Apr 2019
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Thanks everyone for the information. Another question: if a higher psi cap is used, wouldn't that raise the pressure in the entire system and not just in the rad? Which would, in turn, put undue pressure /strain on all seals and hoses?
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Junior User
Joined: Mar 2017
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From: Denver, CO
A higher psi cap is not a smart choice! If your system is overheating the a higher psi cap will allow the pressure to rise up to its rated psi tolerance but that just might be enough to damage things.
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Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Yes it does to some degree. A modern radiator can handle greater pressure, but it's possible the OEM heater core may not. If for example had an original, tired engine with many miles or years, I might then be concerned with head gasket damage as well. It works together as a complete system. Another area of dispute is temperature. 160° F. thermostats were known as "summer" thermostats, ordinarily used with straight water. A 50/50 solution of glycol and water provides corrosion protection in addition to freeze protection, this is important even if living in the tropics. Even as far back as '64 the thermostat opening point was 192° F and used a 7 pound cap. Optimal running temperatures are especially important for reducing cylinder bore wear and sludge buildup due to condensation.
Thread Starter
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Tuned
Joined: Apr 2019
Posts: 310
Likes: 50
Yes it does to some degree. A modern radiator can handle greater pressure, but it's possible the OEM heater core may not. If for example had an original, tired engine with many miles or years, I might then be concerned with head gasket damage as well. It works together as a complete system. Another area of dispute is temperature. 160° F. thermostats were known as "summer" thermostats, ordinarily used with straight water. A 50/50 solution of glycol and water provides corrosion protection in addition to freeze protection, this is important even if living in the tropics. Even as far back as '64 the thermostat opening point was 192° F and used a 7 pound cap. Optimal running temperatures are especially important for reducing cylinder bore wear and sludge buildup due to condensation.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Yes, this is where the Shop Manual is invaluable. In the specifications section it will list the factory OEM radiator pressure cap for your truck application. If it originally shipped out with a 7 pound radiator cap, it should not be exceeded. This is one of the most common errors, installing a modern high pressure cap on older applications.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Yes, this is where the Shop Manual is invaluable. In the specifications section it will list the factory OEM radiator pressure cap for your truck application. If it originally shipped out with a 7 pound radiator cap, it should not be exceeded. This is one of the most common errors, installing a modern high pressure cap on older applications.
It was common back in the day that if the radiator was sent out for a leak repair it also got a lower psi cap.
Yes do check the shop book
Dave - - - -
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Everything should be in good shape new, coming from the factory shouldn't it? If they used a 7 lb cap, that's what I would use.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Who has a factory book to look up what it should be so this could be put to rest?
Dave ----